1. Field of the Invention
The present invention relates to an apparatus for measuring the electrical characteristics of an electric circuit, and more particularly, to an apparatus for measuring the characteristics of an electric circuit applicable in a high frequency band, at a high speed.
2. Description of the Related Art
In recent years, higher frequencies have been employed for communication apparatuses. It has been more required to measure the frequency characteristics of an electronic component or a network of an electronic circuit at a high speed. Further, with the development of a spread spectrum communication system and the like, it has been more required to measure the frequency characteristics of an electronic component or an electronic circuit when signals having plural frequencies are input to the electronic component or the electronic circuit.
FIG. 12 is a block diagram of a conventional measuring apparatus. In FIG. 12, a measuring apparatus 1 is composed of a sweep signal generator 2, a one-input two-output switch 3, circulators 4 and 5, two-input one-output switch 6, a band pass filter 7, a signal detector 8, a corrector 9, an indicator 10, a controlling circuit 11, and signal ports P1 and P2. In this case, the output of the sweep signal generator 2 is connected to the switch 3. One output of the switch 3 is connected to the signal port P1 through the circulator 4. The other output of the switch 3 is connected to the signal port P2 through the circulator 5. Further, the circulator 4 is connected to one input of the switch 6. The circulator 5 is connected to the other input of the switch 6. The output of the switch 6 is connected to the indicator 10 through the band-pass filter 7, the signal detector 8, and the corrector 9 in that order. The controlling circuit 11 is connected to the sweep signal generator 2, the band-pass filter 7, the corrector 9, and the indicator 10. Outside the measuring apparatus 1, the signal port P1 is connected to the first terminal 12a of an external object 12, and the signal port P2 to the second terminal 12b of the object 12, respectively. In this case, the sweep signal generator 2 is so configured that its oscillation frequency can be swept in the order toward the higher frequency. The band-pass filter 7 is so configured that its pass-band can be changed in correspondence to the oscillation frequency of the sweeping signal generator 2 to make only the signal having the oscillation frequency form the sweep signal generator 2 to pass.
In the measuring apparatus 1 configured as described above, for example, if it is desired to measure the pass-characteristics (S21) ranging from the first terminal 12a of the object 12 to the second terminal 12b, the sweep signal generator 2 and the circulator 4 are connected by means of the switch 3, and the circulator 5 and the band-pass filter 7 are connected by means of the switch 6. The controlling circuit 11 causes the oscillation frequency of the sweep signal generator 2 to be swept in a predetermined frequency range in the order toward the higher frequency. The signal from the sweep signal generator 2, going through the switch 3 and the circulator 4, is output from the measuring apparatus 1 trough the signal port P1, and input to the object 12 through the first terminal 12a. The signal, passed through the object 12, is output through the second terminal 12b, and returned to the measuring apparatus 1 through the signal port P2. The signal returned to the measuring apparatus 1, through the circulator 5, the switch 6, and the band-pass filter 7 for passing only the signal having the oscillation frequency of the sweep signal generator 2, is input to the signal detector 8, where the amplitude and the phase are detected. The amplitude and the phase of the signal detected by the signal detector 8 is corrected by means of the corrector 9 using the calibration values determined previously in the state that the object 12 is absent and the signal ports P1 and P2 are directly connected, and displayed on the indicator 10.
As seen in the above description, the oscillation frequency of the sweep signal generator 2 is swept in the order toward the higher frequency, and detected, corrected, and displayed each sweeping cycle. Thus, the dependence of the pass-characteristics of the object 12 on the frequency are displayed on the indicator 10.
In the above example, described is the configuration of the measuring apparatus 1 by which the pass-characteristics ranging from the first terminal 12a to the second terminal 12b of the object 12 are measured. However, by combination of the switches 3 and 6, the configuration can be employed by which the pass-characteristics (S12) of the object 12 ranging from the second terminal 12b thereof to the first terminal 12a, or the reflection characteristics (S11 and S22) of the object 12 in the first terminal 12a and the second terminal 12b are measured.
However, in the measuring apparatus 1 shown in FIG. 12, it is indispensable to sweep the oscillation frequency of the sweep signal generator 2. Thus, for the sweeping, a time-period is required. Thus, there is the problem that as the band of frequencies for measurement is wider, or the measurement point number of the frequency is greater, the sweeping time is longer, that is, the measurement time is greater.
As regards the pass-characteristics and the reflection characteristics of the object such as S11 and S21, only one characteristic of the object can be measured at one time. Accordingly, the measurement needs to be repeated for the respective characteristics. It is troublesome that a still longer time-period is required for the measurement.
Further, the frequency characteristic can be measured only in the state that a signal having one frequency is input to the object at one time. Thus, caused is the problem that if signals having at least two frequencies are input to the object at the same time, the characteristics can not be measured.
The present invention provides a measuring apparatus by which plural characteristics at plural frequency can be measured at the same time, and moreover, non-linear characteristics given in the state that plural signals are input can be measured.
To achieve the above object, the measuring apparatus comprises a multi-carrier generator for generating a multi-carrier signal composed of signals having plural frequencies and being orthogonal to each other;
an output for sending the multi-carrier signal to an external object; an input for receiving the multi-carrier signal output from the object; and a frequency characteristic measuring apparatus for measuring the electrical characteristics at the respective frequencies of the object, based on the received multi-carrier signal.
Preferably, the multi-carrier generator is operative to generate plural multi-carrier signals which are orthogonal to each other.
The output may have plural ports for transmitting the plural multi-carrier signals to the object in parallel.
The input may have plural ports for receiving the plural multi-carrier signals. output from the object in parallel.
Preferably, the frequency characteristic measuring apparatus is operative to measure plural kinds of characteristics of the object based on the received plural multi-carrier signals.
Also preferably, the multi-carrier signals to be input to the object is swept in a predetermined frequency range.
Preferably, the multi-carrier generator comprises a signal generator for generating a signal having one frequency, a spread code generator for generating a predetermined spread code, and a spectrum spreader for spreading spectrally the signal generated by the signal generator with the spread code generated by the spread code generator, and the frequency characteristic measuring apparatus comprises plural filters corresponding to the frequencies of the respective signals contained in the received multi-carrier signal, and plural signal detectors for measuring the characteristics for the respective signals separated by the plural filters.
Also preferably, the multi-carrier generator comprises a signal generator for generating a signal having one frequency, a data generator for generating a predetermined datum, a modulator for modulating primarily the signal generated by the signal generator with the predetermined datum to form a signal which changes time-dependently in correspondence to the predetermined datum, and a timexe2x80x94frequency converter for converting the modulated signal time-dependently to form a multi-carrier signal composed of signals having plural frequencies, said signals being related principally to the predetermined datum, and, the frequency characteristic measuring apparatus comprises a frequency time converter for frequencyxe2x80x94time converting the received multi-carrier signal, and a signal detector for detecting the difference between the modulated signal and the frequencyxe2x80x94time converted signal, correspondingly to the predetermined datum.
With the above-described configuration, according to the measuring apparatus of the present invention, the plural characteristics at plural frequencies of a measurement object can be measured at the same time, and moreover, the characteristics can be measured in the state that the plural signals are input to the object at the same time.